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In croplands, soil erosion resistance varies with both natural processes and human disturbances. To clarify the temporal variation in soil erosion resistance, nine cropland plots with three treatments (continuous fallow, fallow after tillage and tillage with corn) were established in the dry–hot valley region of China. A total of 144 field runoff simulation experiments were conducted from May to October to measure the soil detachment rate (Dc), rill erodibility (Kr) and critical shear stress (τc). The results revealed that the natural dry—wet alternation had little influence on the continuous-fallowed soil erosion resistance. On the other hand, the tillage disturbance that occurred in May sharply increased the Dc and Kr to 2.24 and 3 times that of the continuous-fallow treatment, respectively. Then, the erosion resistance could be enhanced with surface consolidation for the fallow-after-tillage treatment. However, after three months of fallow, the Kr was still 89.5% of the fresh tilled soil. In contrast, crop growth could significantly improve aggregate stability and reduce the Kr to 38.2% in August and even further to 23.7% in October compared to the fresh tilled soil. It could be concluded that crop growth is more efficient in enhancing erosion resistance than the mechanical effect. The above results would benefit from the accurate modeling of cropland soil erosion dynamics and guide agricultural management in dry–hot climate regions. [ABSTRACT FROM AUTHOR]

Soil erosion resistance is influenced by intrinsic soil properties and multiple external factors. This study investigated the effect of tea planting age on soil resistance to flowing water erosion (reflected by rill erodibility (Kr) and critical shear stress (τc)) in Three Gorges Reservoir Area. One slope farmland (as the control) and five tea plantations cultivated for 3 to 34 years were selected for sampling sites. The results indicated that bulk density (BD), soil cohesion (Coh), water stable aggregate (WSA), mean weight diameter (MWD), soil organic carbon (SOC), litter density (LD), and root mass density (RMD) increased generally with tea planting age. Compared to the control, Kr of tea plantations reduced by 71.1%-85.3%. The temporal variation in soil erosion resistance was controlled greatly by the variations in most near-surface characteristics. Kr decreased with WSA, Coh, LD, RMD, and SOC following a power function (P < 0.01); τc increased with MWD, LD, RMD, and SOC as an exponential function, with BD a power function, and Coh a logarithmic function (P < 0.01). In this study, Kr could be simulated well by WSA and LD with a power function, and τc could be simulated well by MWD and RMD with an exponential function.

In croplands, soil erosion resistance varies with both natural processes and human disturbances. To clarify the temporal variation in soil erosion resistance, nine cropland plots with three treatments (continuous fallow, fallow after tillage and tillage with corn) were established in the dry–hot valley region of China. A total of 144 field runoff simulation experiments were conducted from May to October to measure the soil detachment rate (Dc), rill erodibility (Kr) and critical shear stress (τc). The results revealed that the natural dry—wet alternation had little influence on the continuous-fallowed soil erosion resistance. On the other hand, the tillage disturbance that occurred in May sharply increased the Dc and Kr to 2.24 and 3 times that of the continuous-fallow treatment, respectively. Then, the erosion resistance could be enhanced with surface consolidation for the fallow-after-tillage treatment. However, after three months of fallow, the Kr was still 89.5% of the fresh tilled soil. In contrast, crop growth could significantly improve aggregate stability and reduce the Kr to 38.2% in August and even further to 23.7% in October compared to the fresh tilled soil. It could be concluded that crop growth is more efficient in enhancing erosion resistance than the mechanical effect. The above results would benefit from the accurate modeling of cropland soil erosion dynamics and guide agricultural management in dry–hot climate regions.

Plant roots play an important role in reducing soil detachment and increasing soil erosion resistance. Current studies have mainly focused on the quantification of the soil detachment rate (SDR). However, few studies have been conducted to explore the variation in the SDR and root effects during the soil detachment process. In this study, undisturbed soil samples were collected from four shrublands (with the main species Caragana korshinskii, C. korshinskii mixed with Agropyron cristatum, C. korshinskii mixed with Bothriochloa ischaemum, and C. korshinskii mixed with Artemisia gmelinii) and three grasslands (with the main species B. ischaemum, B. ischaemum mixed with A. cristatum, and B. ischaemum mixed with A. gmelinii) on the Loess Plateau, China. The samples were subjected to flow scouring through hydraulic flume experiments under six different shear stresses. The duration of this experiment was 6 min, and the SDR of each minute was estimated. The results showed that the SDR of shrubland was higher than that of grassland in each detachment process. The dominant factors affecting SDR gradually changed from the root–soil composite properties to the hydrodynamic parameters in this process. The effect of roots on the SDR was stronger than that of soil properties in the root–soil composite. In the early detachment stage, the 0–2 mm fine roots had the strongest effect on the SDR, while it was affected by the combined effect of fine roots and coarse roots in the later stage. When the fibrous roots were mixed with the tap roots, the fibrous roots had a significant negative effect on the SDR and mainly affected the early detachment stage. However, the tap roots had a weak effect in all stages. With the detachment process, the soil erosion resistance first increased and then stabilized, and the variations were mainly concentrated from 0 to 3 min. The roots mainly affected the SDR and soil erosion resistance by influencing rill erodibility parameters. [ABSTRACT FROM AUTHOR]

Biochar addition can change the physiochemical properties of soil, thus likely influencing soil's resistance to rill flow (reflected by rill erodibility (K r , s m−1) and critical shear stress (τ c , Pa). However, the persistent time effects of biochar on K r and τ c have remained unexplored. This study aimed to assess the impact of biochar composed of apple branches on K r and τ c , and to investigate the relationships between K r , τ c and soil properties. The undisturbed soil core samples to a depth of 5 cm were collected from field plots that had received biochar at rates of 0, 1, 2.5, 4, 5.5, and 7 % (w/w) after 1, 2, and 3 years, respectively. The K r and τ c of these samples were evaluated through a flume experiment, with scouring soil samples under three flow discharges (e.g., 0.00025, 0.00045, and 0.00065 m−3 s−1) and five slope gradients (e.g., 5.24, 8.75, 17.63, 26.79, and 40.40 %). The results revealed that the ranges of K r and τ c for no biochar treatments varied from 0.1947 to 0.2107 s m−1 and 1.6971–1.7314 Pa, with the averaged values of 0.2007 s m−1 and 1.7100 Pa, respectively. Compared with no biochar addition, the addition of 1–4 % biochar after 1–2 years generally resulted in a reduction in K r ranging from 20 % to 59 %, while increasing τ c by 2–4 %. Conversely, 5.5 and 7 % biochar addition increased K r by 31 and 5 %, and reduced τ c by 12 and 6 %. All biochar treatments after 3 years resulted in a 51 % reduction in K r and a 5 % increase in τ c relative to bare soil, showing an increasing trend with an increasing biochar addition rate. The fluctuations in K r and τ c could be elucidated by changes in cohesion (COH) and mean weight diameter of soil aggregates (MWD), with COH (total effect of −0.32 and 0.17, P <0.01) and MWD (total effect of −0.13 and 0.37, P <0.01) serving as reliable estimators of K r and τ c during the 1–2 years following biochar addition. After biochar addition for 3 years, total organic carbon (TOC) (total effect of −0.45 and 0.10, P <0.01) emerged as a significant factor influencing K r and τ c , making TOC a potential p r edictor of K r and τ c. The results demonstrate that biochar may be an effective measure for enhancing soil resistance to erosion on the Loess Plateau, especially when applied over the long term. • 1–4 % biochar increased rill erodibility (K r) but result was oppsite for 5.5 % and 7 % additions after 1–2 years. • Biochar addition after 3 years enhanced soil erosion resistance for all rates. • Total organic carbon (TOC) significantly affected K r as biochar addition duration increased. • MWD, soil cohesion and TOC could be used to estimate K r under biochar addition. [ABSTRACT FROM AUTHOR]

Understanding the influence of vegetation types on soil particle-size distribution (PSD) is essential to evaluate the effects of sediment control by vegetation restoration. In this work, we studied the effects of different vegetation types, including bare land, meadow, shrub and forest on soil PSD in Jiangjiagou gully, Yunnan province, China. A total of 60 soil samples were collected and analyzed for soil particle size distribution using the laser diffraction method. Fractal theory was used to calculate multifractal parameters. The volume fraction of silt particles in shrub and forest is significantly higher than that in bare land, meadow, whereas the total volume fraction of sand particles in bare land and meadow exceed that in shrub and forest. The soil particle size distribution along soil layers has no significant difference in each vegetation type. The volumetric fractal dimension is significantly higher in forest and shrub than in bare land and grassland, but there is no significant difference between forest and shrub. In addition, soil erosion resistance exhibits significant differences of forest > shrub > grassland > bare land. Multifractal parameters are highest in bare land except for multifractal spectrum values (f (αmax) and f (αmin)) and the maximum value of singularity index (αmin). All generalized dimensions spectra curves of the PSD are sigmoidal, whereas the singular spectrum function shows an asymmetric upward convex curve. Furthermore, soil erosion resistance has significant relationships with multifractal parameters. Our results suggest that multifractal parameters of the soil PSD can predict its anti-ability to erosion. This study also provides an important insight for the evaluation of soil structure improvement and the effects of erosion control by vegetation restoration in dry-hot valley areas.

• (1) The impacts of biocrusts on soil erodibility were investigated in the humid region of TGRA. • (2) CSEI decreased as a threshold-based nonlinear function with the increase of biocrusts coverage. • (3) Variation in soil erodibility was controlled by the differences in BC th , soil texture, and SOM. • (4) Biocrusts decreased soil erodibility was dominant through its consolidation effect in TGRA. Biological soil crusts (Biocrusts) play a significant role in controlling soil erosion by regulating soil erodibility. Nevertheless, affected by the regional climate, soil types, and biocrusts types, the influence mechanism of biocrusts on soil credibility, may be completely different in different regions. Most previous studies regarding the effects of biocrusts on soil erodibility were carried out in dryland regions, and little is known in humid regions where biocrusts are well developed. Therefore, this study was conducted to quantify the variation in soil erodibility, reflected by soil cohesion (Coh), penetration resistance (PR), saturated hydraulic conductivity (K s), mean weight diameter (MWD), mean number of drop impact (MND), soil erodibility of K factor (K), structural stability index (SSI), and a comprehensive soil erodibility index (CSEI), with biocrusts coverage and reveal the influence mechanism of biocrusts on soil erodibility of economic fruit forests land in the Three Gorges Reservoir area (TGRA). Six economic fruit forests land of Citrus sinensis with different biocrusts coverages (0–20%, 20%-40%, 40%-60%, 60%-80%, 80%-100%) and without biocrusts (as control) were selected as the testing sites. The results showed that the development of biocrusts significantly decreased soil erodibility. Compared to Citrus sinensis land without biocrusts, the development of biocrusts increased Coh , K s, MWD , MND , and SSI significantly, whereas decreased PR , K , and CSEI significantly. The reductions in CSEI varied from 19% to 66%. Moreover, with the increase of biocrusts coverage, CSEI exhibited a changing pattern of decreasing first and then reaching a stable stage when coverage was approximately greater than 20%. In particular, variation in CSEI with biocrusts coverage was dominantly controlled by the differences in biocrusts thickness, soil particle distribution, and organic matter content. Biocrusts thickness played the most critical role via directly bonding or binding soil particles and aggregates. The result is helpful for understanding the process and mechanism of soil erosion controlled by biocrusts, also provides a new idea for the prevention of soil erosion under economic fruit forests in the TGRA. [ABSTRACT FROM AUTHOR]

Maize growth has great effects on soil properties and thus likely induces the changes in soil erosion resistance on sloping farmland. However, temporal variation of soil erosion resistance during the growth stages of maize is still unclear in the mountainous yellow soil area where maize is the dominant crop. In this study, four maize plots (MP) and four bare land plots (CK) were conducted to investigate soil erosion resistance, and multiple indicators of soil erosion resistance were measured including the total soil anti‐scourability (TAS), mean weight diameter (MWD), soil erodibility K factor and soil shear strength (SH). A comprehensive soil erosion resistance index (CSERI) was employed to quantify the temporal variation of soil erosion resistance during the growth stages of maize (seedling stage, SS; jointing stage, JS; tasselling stage, TS; maturing stage, MS). The results showed that TAS, MWD, SH increased significantly with maize growth and SH decreased when at MS. But K factor decreased significantly over time. CSERI increased significantly during the growth stages of maize and the CSERI of JS, TS, MS increased on average by 74.72, 180.68 and 234.57% than that of SS. Compared to CK, CSERI of MP increased by 49.90, 66.82, 55.60 and 38.61% during the growth stages of maize. The temporal variation of soil erosion resistance was closely related to the changes in maize cover, maize roots and soil organic carbon. The findings demonstrated that it is necessary to consider the temporal variation of soil erosion resistance in the mountainous yellow soil area. [ABSTRACT FROM AUTHOR]

• Stream power is the optimal hydraulic index for predicting Dc during farmland abandonment. • RSAD driven by farmland abandonment would better reflect the effect of roots on Dc. • Dc could be modeled by stream power, root surface area density, soil cohesion, and D 50. Vegetation restoration significantly affected root traits during farmland abandonment, thereby considerably altering the soil detachment process. However, few studies have investigated the effects of root traits on soil detachment capacity under different ages of farmland abandonment. To examine the effects of root trait changes caused by vegetation restoration on soil detachment capacity by overland flow (Dc) and soil resistance to erosion under different ages of farmland abandonment, flow scouring tests under five shear stress levels (2.80–12.95 Pa) were conducted on 125 undisturbed soil samples collected using an indoor variable slope flume. The results showed that, compared to slope farmland, the root traits of abandoned farmland (5, 12, 24, and 36 years) increased considerably, and the Dc and erodibility decreased by 51.3–93.9 % and 61.8–94.1 %, respectively. The critical shear stress of abandoned farmland gradually increased with the age of farmland abandonment, but remained less than that of slope farmland. Among hydraulic parameters, stream power was the optimal index for predicting Dc , while among root morphological traits, root surface area density (RSAD) was the best indicator for predicting Dc. The median soil particle size (D 50) and cohesion are important factors that affect soil detachment. According to the Water Erosion Prediction Project (WEPP) model, Dc can be predicted using the RSAD and soil cohesion (R 2 = 0.95, NSE = 0.95). In addition, a new model was established to estimate the soil detachment capacity based on D 50 (R 2 = 0.97, NSE = 0.97). In the present study, the performance of the model was improved compared with that of previous studies. [ABSTRACT FROM AUTHOR]

Biological soil crusts (biocrusts) are important landscape components that exist in various climates and habitats. The roles of biocrusts in numerous soil processes have been predominantly recognized in many dryland regions worldwide. However, little is known about their effects on soil detachment process by overland flow, especially in humid climates. This study quantified the effects of moss-dominated biocrusts on soil detachment capacity (Dc) and soil erosion resistance to flowing water in the Three Gorges Reservoir Area which holds a subtropical humid climate. Potential factors driving soil detachment variation and their influencing mechanism were analyzed and elucidated. We designed five levels of coverage treatments (1%–20%, 20%–40%, 40%–60%, 60%–80%, and 80%–100%) and a nearby bare land as control in a moss-dominated site. Undisturbed soil samples were taken and subjected to water flow scouring in a hydraulic flume under six shear stresses ranging from 4.89 to 17.99 Pa. The results indicated that mean Dc of moss-covered soil varied from 0.008 to 0.081 kg m−2 s−1, which was 1.9 to 21.0 times lower than that of bare soil (0.160 kg m−2 s−1). Rill erodibility (Kr) of moss-covered soil ranged from 0.0095 to 0.0009 s m−1, which was 2 to 20 times lower than that of bare soil (0.0187 s m−1). Both relative soil detachment rate and Kr showed an exponential decay with increasing moss coverage, whereas the critical shear stress (τc) for different moss coverage levels did not differ significantly. Moss coverage, soil cohesion, and sand content were key factors affecting Dc, while moss coverage and soil bulk density were key factors affecting Kr. A power function of flow shear stress, soil cohesion, and moss coverage fitted well to estimate Dc (NSE=0.947). Our findings implied that biocrusts prevented soil detachment directly by their physical cover and indirectly by soil properties modification. Biocrusts could be rehabilitated as a promising soil conservation measure during ecological recovery to enhance soil erosion resistance in the Three Gorges Reservoir Area. [ABSTRACT FROM AUTHOR]

Plant litter can either cover on soil surface or be incorporated into top‐soil layer in natural ecosystems. Their effects on infiltration and soil erosion are likely quite different. This study was performed to compare the effects of litter covering on soil surface and being incorporated into top‐soil layer on infiltration and soil erosion under simulated rainfall. Four litter types (needle‐leaf, broad‐leaf, brush, and herb) were collected from fields and applied to cover on soil surface or to be incorporated into top‐soil layer (5 cm) at the same rate (0.2 kg/m2). The simulated rainfalls (40 and 80 mm/hr) were run at two slope angles (10° and 20°). The results showed that the mean infiltration rate of litter covering treatment was 1.4 times as great as that of litter incorporated. Litter covering enhanced infiltration via protecting surface from soil sealing. Whereas, litter incorporation affected infiltration by its water repellency. Soil erosion of litter incorporated treatment was 5.4 times as large as that of litter covered treatment, which was attributed to the changes in surface litter coverage and soil erosion resistance. Litter type affected soil erosion through the variations in litter coverage and litter morphology. For litter covering treatment, litter coverage can explain the major variance of soil loss on the slopes. Whereas, for litter incorporated treatment, both the influences of litter coverage and litter length on soil erosion resistance were considered necessary to well explain the variance of soil loss. The results also showed that the benefits of litter to control soil erosion declined with rainfall intensity and slope gradient for both covering and incorporated treatments. The results of this study are helpful to understand the mechanisms of litter influencing hydrological and erosion processes on hillslopes. [ABSTRACT FROM AUTHOR]

The effect of soil contamination with synthetic detergents (SD) Labomid-203, MS-8 and ML-51 in combination with potassium monoborate (MBP) on the change in the potential of soil erosion resistance (PER) was evaluated. PER characterizes the soil resistance to water erosion and is equal to the energy of a water jet acting perpendicular to the soil surface, required for the destruction and removal of a unit of soil mass from the area of its natural occurrence. Soil water retention curve (SWRC) and hydraulic conductivity were selected for the research as parameters determining soil erodibility. SWRC and moisture conductivity function are dependent on the surface tension and viscosity of the moisture in the soil, which are changed on soil contamination with surfactants of washing solutions. Integrating the expression for SWRC in the range of moisture content values from a fixed initial value to the value, corresponding to the complete filling of soil pores with moisture, gave the result correlating with the energy determining the potential for erosion resistance. Soil contamination with SD and MBP led to the significant decrease in soil erosion resistance, which is particularly evident at low moisture values. The largest decrease in soil erosion resistance (by an average of 39.6%) was caused by MS-8 (1.0% MS-8, 0.3% MBP). The smallest decrease in soil erosion resistance (by an average of 12.4%) was caused by ML-51 (0.5% ML-51, 0.1% MBP). The experiments were carried out with dark-gray and light-gray forest soils of the Chuvash Republic (Russia). [ABSTRACT FROM AUTHOR]

Aims: Biological soil crusts (biocrusts) are soil-surface communities in drylands, dominated by cyanobacteria, mosses, and lichens. They provide key ecosystem functions by increasing soil stability and influencing soil hydrologic, nutrient, and carbon cycles. Because of this, methods to reestablish biocrusts in damaged drylands are needed. Here we test the reintroduction of field-collected vs. greenhouse-cultured biocrusts for rehabilitation.Methods: We collected biocrusts for 1) direct reapplication, and 2) artificial cultivation under varying hydration regimes. We added field-collected and cultivated biocrusts (with and without hardening treatments) to bare field plots and monitored establishment.Results: Both field-collected and cultivated cyanobacteria increased cover dramatically during the experimental period. Cultivated biocrusts established more rapidly than field-collected biocrusts, attaining ~82% cover in only one year, but addition of field-collected biocrusts led to higher species richness, biomass (as assessed by chlorophyll a) and level of development. Mosses and lichens did not establish well in either case, but late successional cover was affected by hardening and culture conditions.Conclusions: This study provides further evidence that it is possible to culture biocrust components from later successional materials and reestablish cultured organisms in the field. However, more research is needed into effective reclamation techniques. [ABSTRACT FROM AUTHOR]

Plant roots significantly affect soil erosion, while few works have pursued why root-penetrated soil obtained higher soil erosion resistance as compared with plain soil. For the purpose to investigate the relative contribution of root physical enlacing (root net-link and root-soil bond functions) and root biochemistrical exudates to soil erosion resistance. This study selected Purple alfalfa root- and designed root-penetrated Loess soil as study object, and subjected to flow scouring. The results showed that roots could significantly ameliorate soil properties, especially for soil enzymes. Root physical enlacing is the main reason, accounting for 77.7–82.0% of the root total effect in strengthening soil erosion resistance. And of this total, the relative contribution ratio of net-link and soil-root bond functions to soil erosion resistance was 0.71:0.29, averagely. Root surface area density could effectively reflect root physical enlacing effect. This kind of study may provide theoretical explanations for the root reinforcement in the flow-induced erosion regions. [ABSTRACT FROM AUTHOR]

Native grasses that have acceptable forage yield and quality can play an important role in the sustainable development and protection of soil ecosystem. In this study, we investigate a native grass of northern China, Cleistogenes songorica, showing promise for erosion control. We used a rainfall simulation method to compare the effects of C. songorica roots and tall fescue roots ( Festuca arundinacea) on soil erosion in sandy loam field plots with irrigation during establishment in 2011 and under mild or severe drought treatments in 2012 and 2013. Root length (RL), root diameter (RD), soil bulk density (SBD), soil field capacity (FC), sediment yield (SY), and root biomass (RB) of each soil monolith were sampled in the topsoil layer (0-10 cm) with a rectangular geotome. The proportion of stable aggregates in soil and the soil anti-scouring properties were also evaluated. C. songorica had higher RD than tall fescue throughout the experiment and evolved higher RL and RB by 2013. Both C. songorica and tall fescue enhanced the erosion resistance of soil, but C. songorica stabilized soil more effectively than did tall fescue. The proportion of stable soil aggregates was greater in C. songorica plots than in tall fescue grassland under mild drought. The present study shows that C. songorica has great potential to be one of the biological resources for soil erosion resistance, water and soil conservation in arid and semi-arid areas. [ABSTRACT FROM AUTHOR]

Soil erosion resistance of gully head determines gully headcut process and further affects gully erosion. However, few studies were conducted to clarify the vertical change in soil resistance of gully heads and its influencing factors, which is not conducive to the revelation of gully erosion mechanism and gully erosion prevention. Therefore, this study aimed to investigate the vertical change in soil resistance of six kinds of typical gully heads developed in farmland (Gf1, Gf2), woodland (Gw), grassland (Gg), abandoned land (Ga) and stable gully channel (Gz) and its influencing factors in the Mollisols region of Northeast China. Soil samples were collected at seven soil depths (0–10 cm, 10–30 cm, 30–50 cm, 50–80 cm, 80–120 cm, 120–160 cm, and 160–200 cm) of each type of gully heads (including three repetitions) to measure soil and root properties. Soil detachment rate (Dr) of gully head at seven soil depths was determined by a hydraulic flume experiment under five runoff shear stresses (4.02–10.89 Pa), and then soil erodibility (K) and critical shear stress (τ 0) of gully heads at seven soil depths were calculated by the equation [ Dr=K ·(τ-τ 0)]. Results showed that Dr and K of six types of gully heads increased firstly and then declined with soil depth increased and the most erodible position occurred at a changed depth of 50–100 cm of gully heads. On average, Dr of Gz was significantly 1.6–9.3 times greater than that of other types of gully heads. Dr of all gully heads was better simulated by stream power than by runoff velocity and runoff shear stress, and it was positively related to soil disintegration rate (DR) and negatively related to soil bulk density (SBD), saturated hydraulic conductivity (SHC), soil shear strength (SSS), mean weight diameter of aggregate (MWD) and root length density (RLD) significantly. The mean K s of Gz and Gg were 1.5–7.8 times greater than that of other types of gully heads, and the K was positively related to DR but negatively related to SHC , SSS , MWD and RLD. τ 0 showed a great fluctuation with soil layer and no significant difference occurred among six types of gully heads. τ 0 was only related with SHC. Soil properties have the larger effect on Dr and K of gully heads than root characteristics, implying that it is not reliable to use only vegetation to control the gully headcut. It is suggested that the first consideration should be given to preventing soil from runoff scouring and improving soil erosion resistance of gully head. • Soil erosion resistance of gully heads in different land uses was quantified. • Soil detachment and erodibility of gully heads decreased and then increased with soil depth. • The most erodible position of gully head occurred at the depth of 50–100 cm. • RF showed that soil properties had larger effect on soil resistance of gully head than roots. [ABSTRACT FROM AUTHOR]

Land use type can impact soil properties and the characteristics of plant community, which in turn likely affect soil erodibility. The irrational land use induced by the fast conversion from natural forestland to cropland certainly leads to serious soil erosion. Few studies have been conducted to assess the potential effect of land use type on soil erodibility at small watershed scale. The aim of this study was to quantify the effects of six typical land use types on soil erodibility reflected by soil penetration resistance (PR), mean weigh diameter (MWD), mean number of drop impact (MND), slaking rate (SR), soil erodibility of K factor, soil organic matter content (SOM), soil structural stability index (SSI), soil cohesion (Coh), saturated hydraulic conductivity (K s) and an integrated comprehensive soil erodibility index (CSEI) in a small watershed of rolling hill northeast China. The results revealed that MWD , MND , SOM , Coh and K s varied significantly with land use type, with their maximum appeared in forest belt and their minimum occurred in road. The measured PR and SR exhibited an opposite trend. The calculated K factor and SSI were relatively stable or slightly fluctuating with land use type. Significant differences were found in soil texture, bulk density, root mass density and litter mass density between different land use types. CSEI varied extremely with land use type. CSEI of road was the maximum (0.855), while transverse forest belt had the minimum one (0.136). Compared to road, CSEI decreased by 14.3%, 10.8%, 26.5%, 36.9%, 33.3% and 65.7% for maize, soybean, grassland, shrub land, woodland and longitudinal forest belt, respectively. CSEI was significantly decreased and increased linearly with root mass density and bulk density. The results provide insights to understand the differences in soil erosion under different land use types in agricultural small watershed characterized by rolling hills. • Different changes were detected in nine erodibility indicators with land use type. • CSEI varied significantly with land use type, with road and TFB had the largest and smallest CSEI. • RMD and BD were the dominant factors influencing the variation in CSEI with land use type. [ABSTRACT FROM AUTHOR]

Biological soil crusts (BSCs) cover up to 60 to 70% of the soil surface in grasslands after the 'Grain for Green' project was implemented in 1999 to rehabilitate the Loess Plateau. However, few studies exist that quantify the effects of BSCs on the soil detachment process by overland flow in the Loess Plateau. This study investigated the potential effects of BSCs on the soil detachment capacity ( Dc), and soil resistance to flowing water erosion reflected by rill erodibility and critical shear stress. Two dominant BSC types that developed in the Loess Plateau (the later successional moss and the early successional cyanobacteria mixed with moss) were tested against natural soil samples collected from two abandoned farmland areas. The samples were subjected to flow scouring under six different shear stresses ranging from 7.15 to 24.08 Pa. The results showed that Dc decreased significantly with crust coverage under both moss and mixed crusts. The mean Dc of bare soil (0.823 kg m−2 s−1) was 2.9 to 48.4 times greater than those of moss covered soil (0.017-0.284 kg m−2 s−1), while it (3.142 kg m−2 s−1) was 4.9 to 149.6 times greater than those of mixed covered soil (0.021-0.641 kg m−2 s−1). The relative detachment rate of BSCs compared with bare soils decreased exponentially with increasing BSC coverage for both types of BSCs. The Dc value can be simulated by flow shear stress, cohesion, and BSC coverage using a power function (NSE ≥ 0.59). Rill erodibility also decreased with coverage of both crust types. Rill erodibility of bare soil was 3 to 74 times greater than those of moss covered soil and was 2 to 165 times greater than those of mixed covered soil. Rill erodibility could also be estimated by BSC coverage in the Loess Plateau (NSE ≥ 0.91). The effect of crust coverage on critical shear stress was not significant. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

• Root tensile strength decreased with root diameter with a power law relationship. • Bromus inermis showed the high average tensile strength and soil cohesion. • High root density might help resist extreme external stress. • Bromus inerm is a good candidate to improve soil shear resistance. Plant roots play a key role in soil erosion process, but less studies are focused on analyze the soil erosion resistance in terms of grassland roots mechanical properties. The objective of this study was to examine the root diameter, root density, root tensile strength and soil shear strength for five typical and widely distributed Poaceae grasses in semi-arid regions, thus determine the contribution of roots of artificial grassland to soil erosion resistance. Results showed that the roots of five grasslands were densely distributed in the surface soils (0–10 cm). Bromus inermis had the strongest roots that characterized by the highest average tensile strength (40.2 MPa) The shear strength significantly increased as the vertical stress increased from 50 kPa to 300 kPa, but the degree varied with grassland types. Shear strength was also linearly correlated with root density when vertical pressure reached 300 kPa (p < 0.01, R2 = 0.47), indicating that high root density might help resist extreme external stress. Moreover, Bromus inermis showed a high soil cohesion of 122.7 kPa (next to the highest value of 128.71 kPa in Panicum virgatum). Overall, Bromus inermis showed the highest soil erosion resistance among these five grasslands, could be a good candidate in Poaceae artificial grasslands to improve soil shear strength for topsoil conservation. These findings have potential implications for understanding the contribution of Poaceae grasses' roots on the topsoil reinforcement, and provide a theoretical basis for artificial grassland establishment on soil erosion resistance on the Loess Plateau. [ABSTRACT FROM AUTHOR]

The factors influencing soil erosion may vary with scale. It remains unclear whether the spatial variation in soil erosion resistance is controlled by regional variables (e.g. precipitation, temperature, and vegetation zone) or by local specific variables (e.g. soil properties, root traits, land use, and farming operations) when the study area enlarges from a hillslope or catchment to the regional scale. This study was performed to quantify the spatial variations in soil erosion resistance to flowing water under three typical land uses along a regional transect on the Loess Plateau and to identify whether regional or local specific variables are responsible for these changes. The results indicated that the measured soil detachment capacities (Dc) of cropland exhibited an irregular trend along the regional transect. The Dc of grassland increased with mean annual precipitation, except for two sites (Yijun and Erdos). The measured Dc of woodland displayed an inverted 'U' shape. The changes in rill erodibility (Kr) of three land uses were similar to Dc, whereas no distinguishable trend was found for critical shear stress (τc). No significant correlation was detected between Dc, Kr and τc, and the regional variables. The spatial variation in soil erosion resistance could be explained reasonably by changes in soil properties, root traits, land use, and farming operations, rather than regional variables. The adjustment coefficient of Kr for grassland and woodland could be well simulated by soil cohesion and root mass density (R² = 0.70, P<0.01), and the adjustment coefficient of critical shear stress could be estimated with aggregate stability (R² = 0.57, P<0.01). The results are helpful for quantifying the spatial variation in soil detachment processes by overland flow and to develop process-based erosion model at a regional scale. [ABSTRACT FROM AUTHOR]

In order to clarify the influence of different forest types on soil erosion resistance in water source area of Central Yunnan, with the soils under three different kinds of typical forest in Yizhe watershed as the research object, this paper uses field simulation method and principal component analysis to analyze the soil erosion resistance of three kinds of soils. The results show that there is a significant difference in the shear strength of soil among three types of typical forest, and the size of soil shear strength is in the order of Pinus yunnanensis forest land > mixed broadleaf-conifer forest land > eucalyptus forest land. The difference in the soil erosion coefficient among different forests is not significant, and the soil erosion resistance is highest in mixed broadleaf-conifer forest land (39. 0% ), followed by eucalyptus woodland (37. 0% ) and Pinus yunnanensis forest land (24. 0% ). Under heavy rain intensity and long duration of rainfall, the ability of soil under eucalyptus x Pinus yunnanensis mixed forests to resist disintegration is more obvious. Using principal component analysis to analyze soil erosion resistance of soils under three different forests, we get the comprehensive evaluation model for soil erosion resistance: F-0. 763 Y1 +0. 236Y2. The soil erosion resistance is in the order of mixed broadleaf-conifer forest land (0.150) > eucalyptus forest land (0.127) > Pinus yunnanensis forest land ( - 0. 079), indicating that the mixed forests have better water loss and soil erosion control effect than pure forests. [ABSTRACT FROM AUTHOR]

• Plant litter incorporated in soil has great effects on inhibiting soil detachment process. • Litter incorporation affects the temporal variation in soil detachment capacity through changing soil structure by physical binding and chemical secretion. • Plant litter incorporated in soil can promote the formation of physical soil crust. • Flow shear stress and soil cohesion can well predict soil detachment capacity. Plant litter incorporation into soil is a widespread phenomenon in the natural environment. Accurate estimation of the soil detachment capacity (Dc) driven by overland flow under litter incorporation effects is crucial for improving soil erosion prediction. However, the effects of litter incorporation on soil detachment processes are often ignored, and the temporal variation of Dc under litter incorporation effects remains unclear for grassland in the Loess Plateau of China. In this study, two litter incorporation soil treatments (Bothriochloa ischaemum (L.) Keng. litter, and Artemisia sacrorum Ledeb. litter) and one bare soil treatment (control) were set. Flume tests with flow shear stress ranging from 5.66 to 22.11 Pa were conducted to simulate overland flow scouring and determine the temporal variation of Dc between May 2017 and October 2018 (nine times, a 524-day period). Furthermore, the key factors affecting Dc were identified. Our results showed that the temporal variation in Dc was consistent across the different soil treatments (two litter incorporation treatments and one bare soil control), showing a rapid decline and then fluctuating at a low level, with Dc ranging from 0.115 to 6.876 kg m−2 s−1. Incorporation of litter effectively reduced Dc , with the Dc of soil treatments incorporating litter being 15% to 29% lower than that of bare soil (2.110 kg m−2 s−1). Further analysis showed that the temporal variation in Dc was mainly affected by the development of a physical soil crust. Dc can be successfully estimated using a nonlinear equation incorporating flow shear stress and soil cohesion (R2 = 0.77, NSE = 0.65), which represent the erosive force and soil erosion resistance, respectively. Our study reveals the important role of plant litter in the soil detachment process and aids the understanding of soil erosion pathways. Further studies are needed to investigate the effects of a physical soil crust on the soil detachment process driven by overland flow. [ABSTRACT FROM AUTHOR]

Changes in soil properties caused by artificial vegetation planting is of great interest to both scientists and policy-makers. However, a quantitative understanding of the effects ofCaraganaplanting on soil erodibility is not available. This study selected fiveCaraganaplantations aged 0 (control), 9, 21, 33 and 46 years to assess the erosion resistance ofCaraganasoils using spatio–temporal substitution method in Zhi Fanggou small watershed on the hilly Loess Plateau. Findings showed thatCaraganaplanting significantly reduced soil loss compared with the control. Sediment loss over time was well described by a negative exponential function. On average, about 80% of the soil sediment was lost within the first 3 abrasion minutes. Compared with control, soil bulk density of surface (0–20cm) and middle soil layers (20–40cm) decreased by 8.9% and 18.0%, respectively, but minimal changes occurred in the lower soils (40–60cm). Soil aggregate content and shear strength increased significantly, whereas soil disintegration rate decreased significantly, with a maximal reduction of 357.1% in the middle soil layer. Soil erosion resistance increased 9.3, 4.1 and 4.2 fold in the surface, middle and lower soils, respectively. Linear regression equations could well fit the relationship between soil erosion resistance and soil physical properties, with root biomass. Soil aggregate content and root density were the key factors in the reinforcement of soil erosion resistance forCaraganaplantations on the hilly Loess Plateau. [ABSTRACT FROM PUBLISHER]

Soil's resistance to erosion or its susceptibility to resist detachment is a key parameter in the majority of soil erosion and sediment models. Although soil resistance is a function of both the intrinsic properties of soil and dynamic environmental variables (e.g., soil moisture), the influence of the latter is seldom explicitly incorporated in the definition of soil resistance. The significant and complex role of soil moisture content on erosion resistance is recognized by many studies, however, much of the emphasis regarding the role of soil moisture on sediment yield modeling has been on its impacts on runoff generation rather than on soil resistance. In this paper, we synthesize the existing state of knowledge on the processes and mechanisms by which moisture affects erosion resistance of soil, and highlight the challenges and opportunities associated with incorporating this relation in sediment yield assessment models. Through a detailed analysis of literature, we find that dry soil has the lowest resistance to erosion and thus has a high erodibility, and erosion resistance increases (erodibility decreases) with increasing antecedent moisture content until a certain threshold. After this threshold is reached, soil resistance decreases with further increase in moisture content, and soils become more susceptible to erosion. Next, the study identifies the candidate variables that may be used to quantitatively represent the soil's resistance to erosion vis-à-vis moisture, and discuss the challenges in incorporating this relation in modeling frameworks. As a way forward, through a meta-analysis of published data, we develop an exemplar relation that could be used to represent the variation in erosion resistance with soil moisture content. We find that the parameters of such a relation vary significantly across soil types, thus raising the possibility for developing a soil-type based moisture-resistance relations. Overall, this review underscores the considerable impact of antecedent soil moisture on the erosion resistance of soils, and makes a case for integrating the influence of dynamic soil moisture content on erosion resistance into predictive modeling frameworks. • Erosion resistance of soil is significantly influenced by soil moisture content. • Erosion resistance increases with increasing moisture content until a threshold. • Erosion resistance vs. soil moisture relation depends on soil type. • An exemplar relation to represent erodibility variation with soil moisture is presented. • Including moisture-erodibility relation in models will improve soil loss predictions. [ABSTRACT FROM AUTHOR]

This article presents a study about rainfall-induced consolidation and soil surface sealing effects on soil erosion during concentrated runoff for loess-derived topsoils. The study aims to establish a relationship between soil bulk density and soil erodibility. It discusses that soil consolidation and sealing were simulated by successive simulated rainfall events which is alternated by periods of drying. In addition, measurements of soil detachment were repeated for four different soil moisture contents.

The article discusses the study which focuses on the role played by microbiotic soil crusts in addressing soil erosion of loess-derived soils in a cropland in Belgium. It states that the study's results were gathered through a field survey, which focuses on three factors including the development of non-biological soil surface, the formation of soil through algae and the development of algal mat and evaluating the effect of microbiotic crust to soil erosion. The study reveals that microbiotic soil crusts grow in areas where maize, sugar beet and wheat are planted, therefore entails that soil crusts develop in cropland under temperate climate.

Abstract: The soil''s resistance to concentrated flow erosion is an important factor for predicting rill and (ephemeral) gully erosion rates. While it is often treated as a calibration parameter in process-based soil erosion models, global change studies require the estimation of erosion resistance from measurable soil properties. Several laboratory and field experiments have been conducted to determine the erosion resistance of various types of soils, but no attempts have been made hitherto to summarize all these data and to explore them for general trends. In this study, all available data on the resistance of topsoils to concentrated flow erosion in terms of channel erodibility (Kc) and critical shear stress (τ cr) has been collected together with all soil and environmental properties reported in literature to affect the soil erosion resistance. Reported Kc values for cropland topsoils range between 0.002 10−3 s m−1 and 250 10−3 s m−1 (n =470), whereas τ cr values range between 0 and 15 Pa (n =522). It is demonstrated that so far, the heterogeneity of measurement methods, the lack of standardized definitions and the shortcomings of the flow shear stress model hamper the comparability of soil erosion resistance values from different datasets. Nevertheless, combining Kc and τ cr data from different datasets, a general soil erosion resistance ranking for different soil textures can be proposed. The compiled dataset also reveals that tillage practices clearly affect Kc (Kc for conventional tillage>Kc for reduced tillage>Kc for no tillage) but not τ cr. It was concluded that Kc and τ cr are not related to each other and that soil and macro-environmental properties affecting the foremost do not necessarily affect the latter as well and vise versa. Often Kc seems to be a more appropriate parameter than τ cr to represent the differences in soil erosion resistance under various soil and environmental conditions (e.g. bulk density, moisture content, consolidation, tillage). The two parameters represent different quantities and are therefore both needed to characterize the soil''s resistance to concentrated flow erosion. [Copyright &y& Elsevier]

Vegetation growth can stimulate the changes in near soil-surface characteristics during a growing season in arid and semi-arid regions, and hence likely induces the temporal variation in soil erosion resistance, reflected by rill erodibility (K r) and critical shear stress (τ c). This study investigated the temporal variations in soil erosion resistance of steep slopes restored with different vegetation communities on the Chinese Loess Plateau. The undisturbed topsoil samples, taken from one control cropland and seven vegetation communities at steep gully slopes, were scoured in a hydraulic flume under six different flow shear stresses. Sampling was conducted for seven times from April 23 to October 10, 2018. Near soil-surface characteristics were simultaneously determined to identify the major influencing factors for the temporal variation in soil erosion resistance. The results showed that the temporal variations in K r of different vegetation communities differed significantly from that of the control. The relative K r of vegetation-restored soils decreased exponentially over time. The temporal variations in τ c were also significantly different from the control for the vegetated samples. Vegetation restoration was effective to enhance soil erosion resistance, and the grass communities were more effective than shrub communities. Compared to control cropland, the mean K r of vegetation-restored soils decreased by 72%–96%, while the mean τ c increased by 100%–183%. The major factors responsible for the temporal variations in K r and τ c were the seasonal variations in root mass density, soil cohesion, and water stable aggregates. K r decreased exponentially, while τ c increased logarithmically with root mass density, soil cohesion, and water stable aggregates. • Vegetation growth led to seasonal changes in near soil-surface characteristics. • Grass was more effective than shrub to enhance soil erosion resistance at steep slopes. • The relative K r of vegetation-restored soils decreased exponentially over time. • Temporal variation in K r related to root mass, soil cohesion and aggregate stability [ABSTRACT FROM AUTHOR]